Retractable assemblies are manufactured and sold by the group of firms, Endress+Hauser, in a large number of variants, for example, under the designation “Cleanfit H CPA475”.
Retractable assemblies are widely used in analytical measurements technology and process automation. They serve to withdraw probes from a process, and therewith from the medium, and then to reintroduce them back into the process, without process interruption. The probes are secured in an immersion tube and by means of a manual drive or automatically, for example, pneumatically, axially moved between a process position (measuring) and a service position (maintenance, calibrating, rinsing, washing, probe exchange, etc.). These procedures take place within a certain timing cycle or as a function of other determinable or measured parameters.
Probes in the sense of this invention comprise probes with at least one receptacle for at least one sensor for measuring one or more physical or chemical, process variables.
The field of use of retractable assemblies for measuring physical or chemical process variables of a medium, e.g. a medium such as a fluid, especially a liquid, in process technology is large. Sensors are used for determining process variables, wherein the sensors can be, for example, pH-sensors, conductivity sensors, optical or electrochemical sensors for determining a concentration of a substance contained in the medium to be monitored, e.g. O2, CO2, certain ion types, organic compounds, and the like.
If retractable assemblies are used for accommodating a sensor for determining at least one process variable, the sensor can, in the service position, be checked, calibrated, cleaned and/or replaced, wherein the sensor is located, in such case, in the housing interior of the retractable assembly, in a so-called service chamber. In order that the medium is not contaminated by calibration-, rinse- or cleaning liquid, the service chamber is so sealed in the service position relative to the containment, in which the medium is located, that no exchange of medium/liquid can take place. Usually, there is located for this on the media-side end of the housing of the retractable assembly a seal, which, by interacting with a closure element on the immersion tube, prevents exchange of medium/liquid.
From time to time, accretions and fouling can accumulate on the closure element and/or on the mentioned seal. In order durably to prevent transfer of washing, or rinsing, medium into the containment in the service position, seal and closure element must be cleaned from time to time. This requires an open connection of the service chamber to the containment. The process is usually paused for the cleaning. It is, in such case, however, not desired that the immersion tube be located in an undefined position or even be capable of uncontrolled movement between service- and process position. In the process position, an efficient cleaning cannot be assured.